A fuel cell has been proposed as a clean, efficient and environmentally responsible power source for electric vehicles and various other applications. Individual fuel cells can be stacked together in series to form a fuel cell stack for various applications. The fuel cell stack is capable of supplying a quantity of electricity sufficient to power a vehicle. In particular, the fuel cell stack has been identified as a potential alternative for the traditional internal-combustion engine used in modern automobiles.
One type of fuel cell is the polymer electrolyte membrane (PEM) fuel cell. The PEM fuel cell includes three basic components: an electrolyte membrane; and a pair of electrodes, including a cathode and an anode. The electrolyte membrane is sandwiched between the electrodes to form a membrane-electrode-assembly (MEA). The MEA is typically disposed between porous diffusion media (DM), such as carbon fiber paper, which facilitates a delivery of reactants, such as hydrogen to the anode and oxygen to the cathode. In the electrochemical fuel cell reaction, the hydrogen is catalytically oxidized in the anode to generate free protons and electrons. The protons pass through the electrolyte to the cathode. The electrons from the anode cannot pass through the electrolyte membrane, and are instead directed as an electric current to the cathode through an electrical load, such as an electric motor. The protons react with the oxygen and the electrons in the cathode to generate water.
It is also known to use other reactants in the PEM fuel cell such as methanol, for example. Methanol may be catalytically oxidized to form carbon dioxide. Protons from the methanol oxidation are transported across the electrolyte membrane to the cathode where they react with oxygen, typically from air, to generate water. As with the hydrogen PEM fuel cell, electrons are transported as an electric current through the external load, such as the electric motor, from the anode to the cathode.
The electrolyte membrane is typically formed from a layer of ionomer. A typical ionomer is a perfluorosulfonic acid (PFSA) polymer, such as Nafion®, commercially available from the E. I. du Pont de Nemours and Company. The electrodes of the fuel cell are generally formed from a finely divided catalyst. The catalyst may be any electro-catalyst which catalytically supports at least one of an oxidation of hydrogen or methanol and a reduction of oxygen for the fuel cell electrochemical reaction. The catalyst is typically a precious metal such as platinum or another platinum-group metal. The catalyst is generally disposed on a carbon support, such as carbon black particles, and is dispersed in an ionomer.
The electrolyte membrane, electrodes, and DM are disposed between a pair of fuel cell separator plates and sealed, for example, with a gasket providing a substantially fluid-tight seal. Each of the separator plates may have a plurality of channels formed therein for distribution of the reactants and coolant to the fuel cell. The separator plate is typically formed by a conventional process for shaping sheet metal such as stamping, machining, molding, or photo etching through a photolithographic mask, for example. In the case of a bipolar separator plate, the bipolar separator plate is typically formed from a pair of unipolar plates which are then joined. It is also known to form the separator plate from a composite material, such as a graphite composite or graphite-filled polymer. Undesirably, the known methods for forming the separator plates can be costly and time consuming.
It is also known to manufacture separator plates for fuel cells according to conventional foaming processes, such as with reticulated metal foam materials. However, conventional foaming processes yield non-uniform and random (not ordered) three dimensional microstructures. Certain techniques do exist to create ordered three dimensional microstructures, such as stereolithography techniques; however, these techniques typically rely on a bottom-up, layer-by-layer approach which prohibits production volume scalability.
Radiation-cured structures are described by Jacobsen et al. in “Compression behavior of micro-scale truss structures formed from self-propagating polymer waveguides”, Acta Materialia 55, (2007) 6724-6733, the entire disclosure of which is hereby incorporated herein by reference. One method and system of creating radiation-cured structures is disclosed by Jacobsen in U.S. Pat. No. 7,382,959, the entire disclosure of which is hereby incorporated herein by reference. The system includes at least one collimated light source selected to produce a collimated light beam; a reservoir having a photo-monomer adapted to polymerize by the collimated light beam; and a mask having at least one aperture and positioned between the at least one collimated light source and the reservoir. The at least one aperture is adapted to guide a portion of the collimated light beam into the photo-monomer to form the at least one polymer waveguide through a portion of a volume of the photo-monomer. Further radiation-cured structures are disclosed by Jacobsen in U.S. patent application Ser. No. 11/801,908, the entire disclosure of which is hereby incorporated herein by reference. A polymer material that is exposed to radiation and results in a self-focusing or self-trapping of light by formation of polymer waveguides is also described by Kewitsch et al. in U.S. Pat. No. 6,274,288, the entire disclosure of which is hereby incorporated herein by reference.
There is a continuing need for a structure and method of manufacturing separator plates for a fuel cell that optimizes fuel cell durability, minimizes tooling costs, minimizes production costs, and minimizes development time.